Pediatric gastroesophageal reflux (GER) is a common problem, especially in infants. Although it is a benign developmental nuisance in most children, in many it produces morbidity, including inadequate growth, respiratory symptoms, esophagitis, and stricture, which implicate it in as many as two admissions a week to a 250 bed pediatric hospital. Pediatric GER differs in important ways from GER in adults. In addition to the unique developmental aspects, GER beginning in infancy may result in esophageal damage continuing decades longer than that beginning in adulthood. Furthermore, emesis (producing inanition) and functional upper airway obstruction (producing apnea) are causes of mortality from GER in children, in contrast to adults. Developments in technology have allowed increasing refinement of understanding of GER, particularly in adults. However, understanding of pediatric GER is largely at an anecdotal and observational level at present; there are few controlled studies prospectively testing hypotheses derived from these preliminary observations. Rigorous analysis of a number of hypotheses concerning pediatric GER is the immediate aim of this application. It is anticipated that these studies will form the basis for refinement of understanding of the physiologic mechanisms involved in pediatric GER. This probing of pathophysiology must and can be done with rigorous clinical studies, because neither animal nor adult human models of pediatric GER are adequate. The specific aims of this research include evaluation of several aspects of pediatric GER pathophysiology, behavioral manifestations, methodology, and therapeutic manipulations. In particular, methodology for evaluating GER will be analysed be comparing pH probe and computer-assisted gastroesophageal scintigraphy during simultaneous use. Secondly ,the therapeutic efficacy of two different prone positions, of thickening of feedings, and of bethanechol will be studied using pH probe, scintiscanning, and esophageal manometry. Behavioral manifestations of infant GER will be studied using video recording of their behavior and simultaneous multichannel physiologic recording including their intraesophageal pH. The pathophysiologic effects of pacifier use on GER will be studied using pH probe.